This invention relates to compact fluorescent lamps and more particularly to compact fluorescent lamps to be used for sun tanning.
Sun tanning booths normally employ linear fluorescent lamps interiorly coated with a phosphor that emits in the ultraviolet or tanning portion of the spectrum. The phosphors used emit radiation in both a desirable range, i.e., 352 nm, and an undesirable range, i.e., 254 nm. The latter range, which is also known as UV-C emission, is considered to be harmful and the FDA regulates its amount, relative to UV-B emission. In the conventional linear fluorescent lamps usually employed, the soda-lime glass from which the lamp envelopes are made absorbs the undesirable 254 nm radiation. However, when compact fluorescent lamps are prepared from the same soda-lime glass and using the same phosphors, it is found that impermissible amounts of the undesired 254 nm radiation are emitted.
It would be an advance in the art if compact fluorescent lamps could be employed, not only in sun tanning booths, but also in certain medical applications where the application of 352 nm radiation is desirable.
It is, therefore, an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance the use of compact fluorescent lamps.
It is yet another object of the invention to reduce or eliminate the emission of 254 nm radiation from compact fluorescent UV emitting lamps.
These objects are accomplished, in one aspect of the invention, by the provision of a U-shaped compact fluorescent lamp comprising two lamp tubes transparent to a desired wavelength of ultraviolet radiation connected by a bight transparent to the desired wavelength and an undesired wavelength with a modification on the bight opaque to at least the undesired wavelength.
It has been discovered that the unwanted or undesirable radiation emanating from compact fluorescent UV lamps comes from the bight of the lamp. Since both the soda-lime glass and the phosphor are normally good absorbers of 254 nm radiation, provided that the thickness is great enough, it is apparent that it is the manufacturing process that causes the undesired emission. Apparently, this is caused by the fact that during manufacture of the lamps the thickness of the glass in the area of the bight is thinned. Also, the phosphor applied to the area of the bight is less than the thickness of the phosphor on the linear tubes of the lamp. These thinner areas allow the undesired emission of the 254 nm radiation. By applying a modification to the bight that is opaque to the 254 nm radiation, the problem is solved and the convenience of the compact fluorescent lamp is available for both sun tanning and medical operations.